I. Field of the Invention
The present invention relates generally to the field of mail sorting and, more particularly, to a storage bin or tray for receiving and storing mail items, typically letters and flat pieces of mail, in a mail sorting machine having a bucket carousel.
II. Discussion of the Background Art
In modern mail sorting machines, mail items are conveyed by a bucket carousel above a plurality of storage bins or trays constituting sorting outlets of the sorting machine. The mail items are dropped from the buckets into the storage trays by opening the bottoms of the buckets, for example as shown in U.S. Pat. No. 5,290,025.
U.S. Pat. No. 6,648,284 discloses a storage tray for mail items dropped from a bucket carousel of a mail sorting machine. Storage trays of this type have a bottom constituted by a wall inclined between two diametrically opposite corners of the tray, enabling the mail items to be stacked in the bottom of the tray, and enabling the stack of mail items in the bottom of the tray to be held in position, more effectively than when the bottom of the tray is oriented horizontally or perpendicular to the side walls of the tray.
Unfortunately, with trays of the above type, the mail items (in particular open items like magazines) tend to bounce off a side wall of the tray before being jogged into alignment in the bottom of the tray. More specifically, a mail item dropped into the tray tends to turn before it is jogged against a side wall of the tray, which can be detrimental to the remainder of the mail sorting process. In addition, the stability of the stack, and thus how well it stays together, is guaranteed only for flat mail items that are homogeneous, even though current sorting machines are required to sort mail items that are heterogeneous, i.e., of widely differing sizes. Furthermore, the arrangement of such a tray does not make it possible for the stack of mail items to be extracted automatically from the storage tray, which can be necessary during unstacking operations at the inlet of the sorting machine.
Another type of storage bin, disclosed in U.S. Patent Application Publication No. 2006/0113362, and shown in FIG. 1 at 10, has a bottom comprising two walls 12 and 14 that are inclined relative to one another at an angle B to form a V-shape in cross-section. Referring to FIG. 2, it can be seen that each mail item 16 that leaves a bucket 18 follows a path b until it lands in the storage bin 10, with one of the two inclined walls constituting a jogging wall 14 for jogging the mail items into alignment in the bottom of the storage bin, and the other of the two inclined walls of the storage bin constituting a landing wall 12 for receiving the mail items in the bottom of the bin. The jogging wall 14 of the bin is inclined at an angle γ relative to horizontal, such as to be substantially tangential to a point along the path b of the mail item and the landing wall 12 of the bin is inclined at an angle α relative to horizontal such that a mail item 16 lands flat on the landing wall.
While this latter type of bin offers some improvement in terms of preserving the sequence of mail items during automatic bin conveying and bin handling operations, certain extreme stacking conditions have been noted that can affect the quality of the mail stack in such a bin. Some of the conditions that can occur to the mail stack include curving, curling, folding, nesting, and flipping of the mail. These conditions can cause problems with downstream handling of the mail and can require human intervention in order to preserve the integrity of the output. Moreover, the probability of finding folded flimsy mail items is higher at the bottom of the stack in the bin than at the top of the bin because the mail item's leading edge will sometimes come in contact with the wall of the bin prior to contacting the previous mail item.
More specifically, as illustrated in FIG. 2, the average drop path b of a mail item 16 released from a bucket 18 of a mail sorting carousel 20 does not follow the slope of the jogging wall 14. After passing the top edge of the bin 10, the leading edge of the mail item 16 moves away from the wall 14. This relationship between the average drop path and the jogging wall increases the probability of having curved or curled mail items in the stack. The inventors have found that, at the bottom of the stack, the probability of finding flimsy mail items in a folded condition is greater than at the top of the stack, possibly due to variations in the motion of specific mail items within the gap between the average drop path b and the jogging wall 14. In the case of a flats sorting system, the amount of mail items that are bound or stapled is much greater than in the case of a first class mail sorting system. So the average thickness of flats mail is bigger at the binding side than the open side, which further increases the probability of curved mail, as the mail binding edge of some flats mail touches the wall outside the relative mail/wall friction cone, and as the stack height gets bigger. In other words, the probability of curved mail items appears to increase with the height of the mail stack.